Field
The present invention relates to a fuel cell vehicle and a control method therefor.
Related Art
There are known fuel cell systems for fuel cell vehicles and the like which run with a motor driven by electric energy generated by a fuel cell. In a fuel cell system described in JP2011-18485A, supply of oxygen-containing gas (air) to the fuel cell, where oxygen is one of reactant gases of the fuel cell, is performed by an air compressor (hereinafter, also referred to as ‘ACP’). An ACP is driven by an ACP motor which is controlled in rotations in response to electric power supplied from an ACP inverter. For example, an increase in air flow rate of the ACP is fulfilled by controlling the ACP inverter for power running of the ACP motor so that the rotation speed of the ACP motor is increased. Also, a decrease in the air flow rate of the ACP is fulfilled by controlling the ACP inverter for regenerative braking of the ACP motor.
However, permissive power-running power for driving the ACP motor, if an output from fuel cells is excluded, is limited by power (hereinafter, also referred to as ‘dischargeable power’ or ‘battery-dischargeable power’) that can be supplied from, a secondary battery provided as a backup of the fuel cell. Therefore, torque of the ACP motor (hereinafter, also referred to as ‘ACP torque’) is, in general, also limited in its upper-limit value (hereinafter, also referred to as ‘upper-limit guard value’) in response to the limited value of the battery dischargeable power. Similarly, permissive regenerative power of the ACP motor is also limited by power that can be charged to the secondary battery (hereinafter, also referred to as ‘chargeable power’ or ‘battery-chargeable power’), and moreover a lower-limit value of the ACP torque of the ACP motor (hereinafter, also referred to as ‘lower-limit guard value’) is also limited. The limitations in these cases mean that the ACP motor cannot be operated (driven) with an ACP torque higher than the upper-limit guard value, and also cannot be operated (regenerated) with an ACP torque lower than the lower-limit guard value. Thus, as an issue involved, the ACP motor cannot be operated in accordance with an instruction of required rotating speed, hence an insufficient responsivity of the ACP motor to instructions of its required rotating speed, i.e., an insufficient ACP responsivity.
For example, in fuel cell vehicles, regenerative braking of a drive motor is basically used as a deceleration mechanism in place of engine breaks in engine-mounted vehicles. Then, in order to obtain larger decelerating power, simply, it can be conceived to employ a mechanism for enhancing a regenerative energy consumption ratio of the drive motor by increasing energy consumption by the ACP, which is done by increasing operations of auxiliary machinery, e.g., rotating speed of the ACP motor. However, there are some cases where the limitation by the upper-limit guard value of the ACP torque as described above makes it impossible to obtain enough increase in energy consumption by the ACP so that enough decelerating power cannot be obtained.
With the accelerator turned off (when a vehicle driver has had a foot off the accelerator pedal), it is desirable that the gas flow rate by the ACP be rapidly lowered to reduce excess oxygen-containing gas within the fuel cells, from the viewpoint of fuel consumption improvement. However, in some cases, due to the limitation by the lower-limit guard value of the ACP torque, it is impossible to fulfill enough regenerative braking of the ACP motor so that enough rapid reduction of the gas flow rate by the ACP cannot be fulfilled.
In addition, in JP2011-18485A, for regenerative braking of the ACP motor, a regenerable power of the ACP motor is calculated based on a power resulting from subtracting the regenerative power of the drive motor from the chargeable power of the secondary battery. Therefore, the regenerable power of the ACP motor can be regarded as being limited, even at most, by the chargeable power of the secondary battery. Thus, with the technique of JP2011-18485A, there is no solution to the above-described issue due to the limitation by the lower-limit guard value of the ACP torque. Furthermore, JP2011-18485A has no description as to the above-described upper-limit guard value of the ACP torque.